Electron discharge device having a laminated and finely reticulated grid structure therein



Jan. 10, 1967 J. E. BEGGS 3,297,902

ELECTRON DISCHARGE DEVICE HAVING A LAMINATED AND FINELY RETICULATED GRID STRUCTURE THEREIN Filed Dec. 22, 1965 2 Sheets-Sheet 2 //7r/em0r James E. 56995 His A from ey' United States Patent ELEQTRON DISCHARGE DEVICE HAVING A LAMINATED AND FINELY RETIQULATEI) GRID STRUCTURE THEREIN James E. Beggs, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Dec. 22, 1965, Ser. No. 522,013 llll Claims. (Cl. 313-348) This is a continuation-in-part of my copending application Serial No. 334,307, filed December 30, 1963. This invention relates to improved grid electrodes for electron discharge devices and particularly to laminated and finely reticulated grid structures for placement close to the cathode of an electron discharge device.

In my Patent 2,680,824, assigned to the assignee of the present invention, a type of electron discharge device having planar electrodes is described and claimed, which device may be miniaturized in structure and conveniently provided with accessible ring-like terminals. For instance, thin wafer-like vacuum tubes of this kind are available having a diameter on the order of 0.32 inch and a height of approximately 0.073 inch. These miniaturized devices are useful at high frequencies because their electrodes are relatively closely spaced reducing electron transit time therebetween. However, a practical limit is reached in the spacing of electrodes close to portions of the electron discharge device which may be heated. For example, a grid electrode in order to be effective should have a spacing between grid conductors comparable to the spacing of the grid from the cathode. A grid determined from these considerations is desirably finely detailed but ordinarily lacks in physical strength because of the detail. When fine wire structures are brought very close to a heated cathode, for example in distances approaching 1 mil from the cathode, the cathode heat has the undesirable effect of warping the grid in an axial direction, sometimes causing contact between the grid and other electrodes while producing variations in tube characteristics.

It is, therefore, an object of the present invention to provide an improved finely reticulated electrode structure having a high degree of mechanical strength which may be placed in close proximity to the cathode of an electron discharge device.

In accordance with the present invention, a finely reticulated grid structure includes a plurality of flat bonded metal laminations each including a substantially similar perforate pattern in registry with patterns of the other laminations. The patterns desirably include spiral-like apertures curving radially away from the central portion of the electrode lamination and having a constant Width for maintaining approximately uniform amplification factor across the face of the electrode. This configuration of pattern in conjunction with the laminated construction provides an electrode structure which is axially rigid when brought as close as one-half mil from an electron discharge device cathode.

In accordance with another feature of the present invention, the electrode structure has a tiered spiral-like aperture configuration. In this construction, portions of the electrode structure between a given set of radii take on the spiral-like form, and a successively greater number of spiral apertures are included between selected successive radii. According to this embodiment of the present invention, a fine structure may be maintained with maximum current flow and heat conduction capabilities between the inner portion and the outer ortion of the electrode.

In accordance with another feature of the present invention, the laminated electrode structure, in addition to including a plurality of electrode metal layers, also ice includes a layer of insulation whereby the function of more than one electrode is provided. Preferably, the insulation is thin, i.e., approximately the same as a single metal lamination, and of reasonably good thermal conductivity so that the metal layers of the electrode on one side of the insulation may serve to cool the layer or layers on the other side of the insulation.

In accordance with another feature of the present invention, successive laminations of the electrode structure are selected from metals which are alternately of one metal and then another to provide maximum strength and electrical performance characteristics.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements and in which:

FIG. 1 is a cross-sectional view of a miniature electron discharge device;

FIG. 2 is a flat side view of a first reticulated lamination of electrode structure formed in accordance with the present invention;

FIG. 3 is a flat side view of a second reticulated lamination of electrode structure formed in accordance with the present invention;

FIG. 4 is a cross-sectional view of a portion of an electrode structure for placement in the FIG. 1 device;

FIG. 5 is a cross-sectional view of a portion of another electrode structure which may be employed in the FIG. 1 type of device;

FIG. 6 illustrates construction for deriving spiral-like apertures for electrode laminations in accordance with the present invention; and

FIG. 7 is a cross-sectional view of a laminated electrode structure in accordance with the present invention including one lamination more finely reticulated than the rest.

In FIG. 1, a miniature electron discharge device 6 having planar electrodes includes an anode electrode 1 spaced from a cathode electrode 2 with the laminated electrode 3 acting as a grid between the anode and the cathode. Flat cathode 2 is heated with a filament 7 secured to the underside thereof. Heat is conducted away from anode 1 by means of a radiator stud 15. Externally accessible electrical terminals for the electrodes of tube 6 are provided by anode ring terminal 16 supporting anode 1, cathode ring terminal 17 supporting cathode 2, and grid ring terminal 18 supporting laminated grid electrode 3. In the event a portion of electrode structure 3 is employed as a screen grid or the like, a further ring terminal 19 is provided.

The cathode surface and the upper surface 20 of the grid terminal 18 lie in a common plane. A metal spacer 21 is placed on upper surface 20 of the electrode terminal 18 to establish the desired gap between electrode 3 and the cathode. The annular insulators 22 between the ring terminals, as well as flat disk 23, are formed of ceramic material completing the tube envelope. A connection to the filament 7 is made via conductor 24 and filament contact 25, the remote end of the filament being connected to cathode ring terminal 17.

In accordance with the present invention, electrode 3, illustrated as a. grid electrode, is laminated in cross-section, each of the laminations preferably taking the form illustrated in FIGS. 2 and 3. Referring to FIG. 2, the electrode lamination is finely perforate or reticulated. While only a ortion of its overall pattern is shown in FIG. 2, it is understood the spiral-like construction is continued around the full circumference of this flat electrode lamination. The lamination is shown greatly enlarged. In actual practice, the entire structure shown is on the order of one-fourth inch in diameter. In forming each such lamination, the configuration is conveniently drawn larger in size and then photographically reduced in the form of a negative on a glass plate or the like. The lamination is formed and bonded with other laminations in accordance with the method of manufacturing such an electrode de scribed and claimed in the copending and currently filed application of August I. Kling and James E. Beggs, Serial No. 334,306. Briefly, the lamination is photo-etched from fiat electrode material, for example, from tungsten, titanium, zirconium, molybdenum, hafnium, tantalum or other conducting refractory metals. Substantially the same pattern is used in forming a plurality of laminations which are then bonded together in substantial registry forming the complete electrode.

Referring further t FIG. 2, an electrode lamination is provided with a central portion 12 including substantially linear apertures separated by straight ribs 13 joined to a circular rib defining the central portion. Outwardly, from the central portion, a number of spiral-like apertures extend from the central portion 12 to a circular rib 11. Then a greater number of spiral-like apertures 9 separated by spiral-like ribs 10 extend from circular rib 11 to an outer circular rib 25 for placement upon spacer 21 in the FIG. 1 electron discharge device, in the case of the bottom lamination. Two tiers of spiral-like apertures are illustrated in FIG. 2, but it is understood a greater numher are frequently desirable.

The spiral-like ribs, for example, ribs 10 in FIG. 2, proceed substantially perpendicularly from their innermost origin, for example, circular rib 11 in FIG. 2, and then curve outwardly with a component tangential to outer ring 25. When a greater number of tiers of such spirallike ribs and apertures are employed, a greater number of ribs appear in each tier so that the current path from the outer circular rib to the inner portion 12 is more direct. Likewise the heat conduction path is shorter. Moreover, the construction of multiple tiers aids in the formation of the finely perforate or reticulated structures. In a particular example employing four tiers instead of two as illustrated in FIG. 2, the first tier surrounding central portion 12 includes 32 ribs, the next tier 64 ribs, the next tier 96 ribs and an outer or fourth tier 128 ribs.

The spiral-like structure in addition to providing a finely divided and reticulated structure of uniform spacing between grid elements, also has the advantage of tending to produce rotation rather than axial movement in the resultant electrode when heated due to close proximity of a cathode, e.g., at a distance of between one-half mil and one mil from a cathode. The construction of such a spiral pattern is illustrated in FIG. 6 where R is the radius of the circular rib or inner portion from which the spiral pattern extends outwardly, and R is the radius of any point along the spiral curve. 0 is the angle between radius R and a line between the center of the construction and the point where the spiral-like pattern originates. The angle for a radius R of any given length can be determined from the following formula:

0 (in radians) I 1 1 Although the spiral-like configuration is very desirable in producing rotation of the electrode structure, some axial movement remains in the case of a unitary spiral-like structure. I have found a laminated structure produces a much stronger and more rigid electrode. In particular a spiral-like laminated electrode has been found to produce no detectable axial movement even when brought as close as one-half mil from the cathode at conventional cathode temperatures. Accordingly axial movement of the electrode structure is no longer a problem in accordance with the device of the present invention, but rather the heat itself may be the limiting factor, as for instance when the electrode is heated to the extent of becoming a primary emitter of electrons. Making outside laminations of titanium or zirconium reduces thermionic emission from an electrode structure. Lamination also aids in the production of finely detailed electrode structure since thin layers are most accurately formed in accordance with the photoetching method set forth and claimed in the aforementioned application, Serial No. 334,306.

A cross-section of a portion of the laminated electrode structures 3 in FIG. 1 is further illustrated in FIG. 4. For example in FIG. 4, three laminations are employed including outer laminations 4 and 5 and inner lamination 8. In each case, the individual laminations desirably take on substantially the same configuration as heretofore illustrated in FIG. 2. The laminations may be formed from various metal materials of the conventional electrode type as hereinbefore mentioned. However, desirable properties are secured when a certain order of lamination is followed. For example, in accordance with one construction, outer laminations 4 and 5 are formed of titanium or zirconium, i.e., a metal having a tendency to keep itself clean through gettering of electron emissive material and gaseous products deposited thereon in the course of electron discharge device operation. The central lamination 8 is desirably formed of a material such as tungsten having advantageous strength and electrical properties at high temperatures. Another advantageous combination comprises, for example, outer laminations 4 and 5 formed of tungsten and an inner lamination formed of molybdenum. Having outer layers of similar metals, i.e., a symmetrical arrangement, tends to balance distortional forces so that no bimetal bending effect is noted. In addition, the electrode structure is given added strength if the metal laminations are oriented such that metal rolling directions are different in each layer. This orientation effect is frequently experienced, adding to the strength of the laminated device, without exercise of special care in determining the rolling direction of the material. The electrode should be laminated up to a height such that the ribs, for example, ribs 10 in FIG. 2, are higher than they are wide, since thickness enhances the tendency of the electrode structure to rotate rather than moving in an axial direction.

In addition to forming a single grid electrode structure in accordance with the foregoing description, the present invention also provides for a multiple reticulated grid structure such as a combined control grid and screen grid in which the two grids are of substantially different thickness and in which the heat conducting and supporting capabilities of the thicker grid are still effective to cool and support the thinner grid. This is accomplished by an interposed insulator of thin dimension, of good heat transfer characteristics and of a configuration sub stantially conforming at least to the grid electrode having the coarser pattern of reticulation. The periphery of the multiple grid structure is in contact with at least one externally accessible terminal, and normally each of the metallic electrodes will be in contact with such a terminal to provide for independent electrical connection thereto and to assist in the dissipation of heat generated in the grid structure. FIG. 5 illustrates such an embodiment of my invention in which the thicker of the grid structures is illustrated as a screen grid and is made up of three laminations, 4, 5 and 8, which may, for example, have substantially the structure described in connection with FIG. 4, in which the intermediate lamination 8 is of one metal, such as tungsten, and the laminations 4 and 5 are of another metal, such as titanium. The thinner grid electrode may be made of a single lamination illustrated at 27, and this lamination may, to advantage, be formed of tungsten. It will be appreciated that other metals may be employed in the grid structure in accordance with the description of the other embodiments of the present invention.

In accordance with an important aspect of the present invention, the two grid structures are separated by a thin lamination 26 of insulating material which has good heat conducting characteristics and good dielectric strength, so that a relatively thin lamination provides electr'cal insulation for the desired voltage and also makes available a heat path of good heat transmissivity from the central regions of the thinner grid member 27 through the insulator 28 and the thicker central portions of the thicker grid to the periphery thereof and thence to the terminal 19. It will be apparent also that substantial heat may be transmitted through the thinner grid itself to the terminal 18. The insulating material may, to advantage, be selected from the group consisting of boron ni tride and beryllia. Both of these materials have good dielectric strength and both are good conductors of heat compared to ceramic materials most frequently used in electron discharge devices. Beryllia is toxic, and this has been considered a disadvantage in the past, but im proved techniques for handling the material are being evolved so that it is possible to utilize this material without undue difiiculty or danger in assembly and use of the device. The insulating material lamination 27 is preferably about the same thickness as the thinner lamination which may, for example, be in the order of .001 inch. The insulating lamination 26 may be .002 inch in thickness and, in any event, is less than the thickness of the thicker metal grid which, in the illustrated embodiment, is composed of the three laminations 4, 5 and 8, each about .002 inch thick. Since the insulating lamination is bonded to both the electrodes throughout the reticulated grid structure of at least the coarser one of the electrodes, it provides a good distributed heat path throughout the central region of the thinner grid for cooling and supporting that grid. As mentioned, the control grid may include additional control conductors of a finer pattern than that of the thicker or screen grid.

As will be readily understood by those skilled in the art, the metal luminations may be bonded together in face-to-face contact with the addition of a bonding or brazing material appropriately selected in accordance with the material of the lamination. For bonding molybdenum to tungsten, the molybdenum may be coated with a thin layer of nickel and bonded at about 1320" C. Titanium may be coated with either nickel, iron or platinum for bonding to titanium or other metal or to boron nitride, for example. The metal grid members may be bonded to boron nitride, for example, by placing a thin layer of barium oxide on the opposed surfaces and assem bling the laminations in contact and heating to a temperature of about 1200 C.

As indicated earlier, the insulating lamination of boron nitride or beryllia preferably has the same reticulated configuration as the metal electrodes and preferably the same as the coarser of the electrodes in the event that one of the electrodes has a finer reticulated pattern. While the insulator may be formed in any desired manner, it may, to advantage, be formed from a thin lamination which is bonded to the adjacent metal members and then blasted away from the grid member openings to form the interposed insulating lamination of the same pattern as the metal. This may be accomplished by using an air jet stream carrying abrasive particles.

In accordance with an additional feature of the present invention, the lower lamination or other lamination of the electrode structure may be more finely perforate than the rest in order to provide added grid control. For example, the bottom lamination for disposition next to the cathode may be thinner and more finely perforate. The combination is illustrated in cross-section in FIG. 7 wherein thin bottom lamination 28 has been added having a fine reticulated structure in addition to the spiral-like pattern of the other laminations. Such finely reticulated structure may take the form of fine circular ribs 14- in the FIG. 3 fiat side view and fine cross ribs 29 in the central section. Making the finely reticulated pattern as a plurality of concentric circles allows them to rotate Without breaking as the whole structure tends to rotate when heated. Making the lamination 28 thinner aids in formation of fine detail according to the process set forth and claimed in the copending Kling and Beggs application Serial No. 334,306. The remaining laminations i, 5 and 8 act as a rigid support and conduct heat away from lamination 28. Lamination 28 is preferably very thin, having a thickness on the order of 0.0005 inch with finely detailed ribs 0.0005 to 0.0008 inch wide.

While I have shown and described several embodiments of my invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from my invention in its broader aspects; and I therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to protect by Letters Patent of the United States is:

1. An electrode structure for an electron discharge device comprising a plurality of flat thin metal laminations each having finely reticulated patterns with at least substantial portions of said patterns being identical wherein said laminations are bonded together with identical portions in substantial registry, at least one lamination for disposition next to a heated cathode in said electron discharge device including a more finely reticulated pattern than the rest of said laminations and which is supported and cooled by the rest of said laminations.

2. The electrode structure according to claim 1 wherein the identical portions of said patterns include radially outwardly extending spiral-like elements, and wherein said more finely reticulated pattern includes a plurality of concentric circles.

3. An electrode structures for an electron discharge device comprising a plurality of fiat metal laminations wherein each lamination has substantially similar fine reticulated pattern, at least substantial portions of the patterns being identical, wherein said laminations are bonded together with identical portions in registry, and wherein said limantions are alternately formed from a first electrode metal material and a second electrode metal material in a symmetrical arrangement for balancing distortional forces.

4. The electrode structure according to claim 3 wherein the first said metal material is selected from the group consisting of titanium and zirconium and the second metal material is tungsten in a lamination disposed between laminations formed of said first-mentioned material.

5. The electrode structure according to claim 3- wherein said first metal material is tungsten and the second metal material is molybdenum in a lamination disposed between laminations of said first-mentioned material.

6. A fine reticulated grid electrode structure for an electron discharge device capable of being closely spaced to heat generating portions of said electron discharge device comprising a plurality of flat reticulated electrode metal laminations each having substantially the same reticulated pattern and bonded together in face-to-face electrically contacting relation with identical portions of said rectiulated pattern in registry to provide a single electrically conducting grid electrode structure, said pattern including curved spiral-like apertures extending outwardly from the central portions of said laminations, said apertures having a substantially constant width.

7. The electrode structure according to claim 6 wherein said reticulated pattern on a plurality of said laminations includes tiers of said spiral-like apertures, a first tier extending from a central portion of said pattern outwardly to a first radius and at least one additional tier extending from said first radius to a second and larger radius.

8. The electrode structure according to claim 6 wherein at least one of said laminations includes a plurality of fine concentric circles of successively larger radii from the central portion of said pattern.

9. A multiple grid structure for an electric discharge device comprising planar reticulated metal grid members and an insulating member interposed between said members and having substantially the same pattern of reticulation as at least one of said grid members, said metal members being bonded in face-to-face relation with the opposite sides of said insulating member, said one grid member being substantially thicker than the other metal grid member and said insulating member being substantially thinner than said one grid member to provide electrical insulation between said metal grid members while providing a path of good thermal conductivity from the central portions of the other of said metal grid members to the rectiulated pattern of said one of said grid members.

10. The combination of claim 9 wherein said insulating member consists essentially of a material selected from the group consisting of boron nitride and beryllia.

11. The combination of claim 9 wherein said one metal grid member is a laminated grid structure of at least three metal layers bonded together in face-to-face relation.

No references cited.

JOHN W. HUCKERT, Primary Excunincr.

A. J. JAMES, Assistant Examiner. 

1. AN ELECTRODE STRUCTURE FOR AN ELECTRON DISCHARGE DEVICE COMPRISING A PLURALITY OF FLAT THIN METAL LAMINATIONS EACH HAVING FINELY RETICULATED PATTERNS WITH AT LEAST SUBONS STANTIAL PORTIONS OF SAID PATTERNS VEING IDENTICAL PORSAID LAMINATIONS ARE BONDED TOGETHER WITH IDENTICAL PORTIONS IN SUBSTANTIAL REGISTRY, AT LEAST ONE LAMINATION FOR DISPOSITION NEXT TO A HEATED CATHODE IN SAID ELECTRON DISCHARGE DEVICE INCLUDING A MORE FINELY RETICULATED PATTERN THAN THE REST OF SAID LIMINATIONS AND WHICH IS SUPPORTED AND COOLED BY THE REST OF SAID LAMINATIONS. 